In small engines of less than 50 horsepower (37.2 kilowatts) such as those employed for garden tractors, lawn mowers, portable generating sets and marine applications it has recently been mandated that such engines be equipped with fuel vapor emission controls.
Small engines used for such applications commonly have the fuel tank disposed approximate the engine for facilitating engine installation on the appliance employing the engine. The more widely used configuration utilizes a gravity feed fuel supply from the tank to the engine carburetor; however, in certain applications on engines approaching 50 horsepower, fuel pumps are employed.
Efforts to provide fuel vapor emission control systems on such small engines and particularly in the aforesaid applications of small engines have required additional components, modifications to the fuel tank and have resulted in significant increases in the cost of installing the engine and fuel system in the appliance. This is particularly the case where it is required to not only prevent fuel vapor emission during periods of engine shutdown but where it is also required to provide a valve which will close the tank make up air vent in the event of disorientation such as tipping or rollover of the appliance in service.
The more widely employed technique of preventing fuel vapor emission from a large engine tank and fuel system has employed a storage canister charged with adsorbent to retain the fuel vapors until the engine is started and the vapors can then be drawn into the engine air inlet and the canister purged by induction of atmospheric air as the vapors are drawn into the engine. Such systems have long been employed in large engines such as in motor vehicles with fuel tanks remote from the engine.
However, it has been found difficult and costly to provide these functions for small engines having fuel tanks which are typically bracket mounted on the engine or the appliance in a position adjacent the engine where it is necessary to keep the volume of the engine and tank to a minimum. This has been particularly difficult to achieve for air cool engines where the engine is closely cowled to provide adequate airflow over the cylinder head for proper cooling. In addition, most small engine applications employ gravity feed fuel tanks which are placed above the engine and thus require a particular configuration for the appliance into which the engine is installed, particularly where the engine is cowled. Thus it has been desired to find a way or means of providing the necessary functions for fuel vapor emission control on small engines, particularly those employing gravity feed fuel tanks without requiring complete retooling for the fuel tank and associated fuel system and tank mounting components.